It is well known that there are a great many allotropes for carbon atom because in the case where carbon atoms are bonded, they take any of the bonding states of SP, SP.sup.2 and SP.sup.3 depending upon the situation.
And as for the crystal comprising carbon atoms, there are known cubic system diamond having SP.sup.3 hybrid orbital; cubic system graphite and trigonal system graphite respectively having SP.sup.2 hybrid orbital; polyyne and cumurene of an amorphous material having SP hybrid orbital; and cardyne comprising said polyyne being partially crystalized or said cumurene being partially crystalized.
In addition, various amorphous carbons. However, they do not have a common structure are known in that they are of complicated structures containing SP, SP.sup.2 or SP.sup.3 hybrid orbital, or a mixture of two or more of these orbitals, and dangling bonds being complicatedly intertwined.
Among the above materials, the cubic system diamond has been generally evaluated as being the most preferred to be industrially utilized for the reasons that it has an extremely high transparency to visible light, an excellent insulating property of about 10.sup.12 .OMEGA..cm, a high heat conductivity of corresponding to 5 folds over that of copper at room temperature and a great refractive index of 2.4, and in addition to these advantages, it has an excellent chemical stability and an extreme hardness. In view of this, there have been made various proposals to prepare a diamond film by way of vapor phase reaction method, and said diamond film is expected to be able to be used a wider application area than is the case of a bulk diamond as disclosed in Japanese Patent Laid-Open Nos. 9100/1983 and 110494/1983 and in Japanese Patent Publication No. 2632/1986.
It is known that there may be prepared a diamond-like carbon film such as carbon film or hydrogen-containing carbon film respectively having similar properties to diamond in the case of using ion beam evaporation method or ion beam sputtering method.
Now, in the case where it is tried to prepare a diamond film by way of vapor phase reaction method, the resulting film often becomes not a single crystal film but a polycrystal film which is clearly euhedral due to diamond crystal with its surface and such surface is accompanied with significant irregularities.
And as for this film, it is extremely difficult to make such irregular surface desirably flattened because of its excellent chemical stability and also of its extreme hardness, and because of this, it may be used only in an extremely limited area although it has excellent optical, electric and mechanical properties.
In addition to the above, there is a limit for the kind of a substrate to be used for the deposition of a diamond thereon because the process of forming a diamond is practiced while maintaining the substrate at elevated temperature of 600.degree. C. to 1000.degree. C., and also because of this, the area for the said film is limited.
On the other hand, as for the diamond-like film to be formed by way of ion beam evaporation method or ion beam sputtering method, its surface is even but there are present carbon multiple bonds and not a few hydrogen atoms therein, and because of this, the said diamond-like film is inferior to a diamond with every respect of transparency to visible light, hardness, chemical stability and electrically insulating property and with the point that it is accompanied with a large local strain.